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Don Schap - BFA, Digital Photography A Photographer Is ForeverLook, I did not create the optical laws of the Universe ... I simply learned to deal with them.
Remember: It is usually the GLASS, not the camera (except for moving to Full Frame), that gives you the most improvement in your photography.flickr® & Sdi

Good diagram and information Don, thats the kin dof stuff I find really handy, have printed it off and put it in my big 3 ring binder of stuff I should know. i go back and flip through it pretty often. each time I try to learn soemthing new i forget something, or I just wonder if I will ever get this figured out!
A-mount from Tokina again you say.....HMMMMMMNNNNNNN now thats intersting.

What can the A900 do w/ a 20mm f/1.8 lens?

There are some striking differences in effect with the 20mm f/1.8 mounted on the A900 body. Basically, the DOF increases under the same situation.

Here a diagram of the change: (Remember same distances, same aperture - f/1.8)

As you can easily see ... not only do you get you get 30-degrees more Field of View (FoV) and nearly 2x the DOF at 10-feet away ... but, you also get a whole bunch more DOF at 20-feet ... almost 10 times more!

If you needed a reason to buy the A900 ... this is a decent one. Plus, if you put the α900 in "CROP" mode, you can whack that DOF right back down to the first diagram ... and get some bokeh in that "bright" shot. It's like having a 20mm and a 30mm lens on your camera.

Last edited by DonSchap; 05-29-2009 at 09:36 PM.

Don Schap - BFA, Digital Photography A Photographer Is ForeverLook, I did not create the optical laws of the Universe ... I simply learned to deal with them.
Remember: It is usually the GLASS, not the camera (except for moving to Full Frame), that gives you the most improvement in your photography.flickr® & Sdi

Concerning the Tokina A-mount issue ...

It is very exciting for SONY DSLRs to have the "Tokina option" in the cards, because then lens prices have a real chance to come down a bit, with competition for everyone's hard earned buck.

Tokina, first and foremost, makes a darn good lens ... definitely worthy of consideration when sized up against a lens of equal capability. That being said, here is the current Tokina lens line up, filter-size, weight and B&H prices (based on the Nikon/Canon mounts):

AT-X 116 Pro DX 11-16mm f/2.8 ø77mm (19.8 oz) - $600

AT-X 165 Pro DX 16-50mm f/2.8 ø77mm (21.5 oz) - $600

AT-X 535 Pro DX 50-135mm f/2.8 ø67mm (29.8 oz) - $530

AT-X 124 AF Pro DX II 12-24mm f/4 ø77mm (19.0 oz) - $550

AT-X M35 Pro DX 35mm f/2.8 Macro ø52mm (12.0 oz) - $400

AT-X M100 AF Pro D 100mm f/2.8 Macro ø55mm (19.0 oz) - $400

AT-X 107 DX Fish-Eye 10-17mm f/3.5-4.5 NA (12.3 oz) - $580

AT-X 840 AF D 80-400mm f/4.5-5.6 ø72 (35.9 oz) - $620

The total of it all is $4280 ... which, honestly, is not bad at all when compared to SONY, SIGMA or TAMRON lens of similar capability. Obviously, Image Quality or IQ will be the real deciding vote (maybe weight) ... but cost, not so much.

Enjoy ... they may see you in December, I guess.

Don Schap - BFA, Digital Photography A Photographer Is ForeverLook, I did not create the optical laws of the Universe ... I simply learned to deal with them.
Remember: It is usually the GLASS, not the camera (except for moving to Full Frame), that gives you the most improvement in your photography.flickr® & Sdi

I'm not taking issue with your feelings on DOF. A big reason for my wanting the A900 is to recover the DOF lost by the crop sensor and not for the 24MP resolution of the sensor. I've written elsewhere that my wish is for a cheaper Full Frame A8** with 12/15MP Sensor. That's enough res for me and it would bring with it the benefit of increased Sensor sensitivity. A 12MP FF Sensor would enable each receptor to capture twice as many pixels which is a huge advantage.

Anyway back to your wide angle. The problem I have with your solution is in the FOV (field of view) rather than DOF (depth of field.
Using your example at school plays and recitals using an
A700 with 20mm lens focused at 20ft the Horizontal FOV is 24ft x 16ft.
A700 with 50mm lens focused at 20ft the Horizontal FOV is 9'7" x 6'5".
A bit of elementary arithmetic shows that the image sizes are different by a factor of 6.
Put a different way, the subjects captured by the 20mm lens will be one sixth the size of those recorded by the 50mm lens.
To get the same FOV with the 20mm you'd need to move in to 8ft.
So yes, the DOF of the 20mm is 10x that of the 50mm but in the swings and roundabouts game the 50mm gains it back in it's FOV.

That's just an opinion, of course. In a different circumstance, photographing a large object for instance the WA wins every time. This boat pic would not have been possible without one (17/35 Minolta at 17mm f2.8).

I will redraw the the first diagram and edit it back into the thread. You are completely correct about proportionality ... and I initially made an error. It will be corrected. Good eye, though.

EDIT: The first diagram has been corrected ... and Sean, you may want to reprint it. It is visually a little more accurate describing the change that takes place with the different sensors.

If you kind of overlay the two ... you immediately see the difference in Field of View or "Angle of View" (FoV) and Depth of Field (DOF)

Overlay of the APS-C sensor vs the A900 FF sensor

Again, Peter, thank for pointing that out and I hope this clears the air. I find it relatively interesting analyzing the shot for its effect ... and finding a good way to mitigate it. I suppose I should say I'm not going to burden the idea of Depth of Field with too many numeric restrictions, but just give a rough idea of the overall effect with aperture and the sensor size.

Last edited by DonSchap; 05-30-2009 at 11:40 AM.

Don Schap - BFA, Digital Photography A Photographer Is ForeverLook, I did not create the optical laws of the Universe ... I simply learned to deal with them.
Remember: It is usually the GLASS, not the camera (except for moving to Full Frame), that gives you the most improvement in your photography.flickr® & Sdi

When there's "noise" in the darkness ...

I guess what got me to consider the 20mm f/1.8 was one night, I was sitting around with the SIGMA 10-20mm f/4-5.6 DC EX mounted and snapping interior shots under "typical" indoor lighting @ 20mm f/5.6 ... which is the brightest aperture that you can get at 20mm with that particular lens.

Word problem:

Shot at ISO-1600 and a shutter speed of 1/15th sec. ... even with noise NR and some High ISO adjustments ... the paneling looked like ... well, unacceptable. I call it "dark noise" ... where the camera is struggling to resolve deep color or shadow.

Moving up to ISO-800 and shutter speed of 1/8th ... again ... the dark noise is just not very good

Taking it to ISO-400 and a shutter speed of 1/4 ... this is really testing Don's steady grip ... the dark noise is still there, but is looking better.

Finally, ISO-200 and a complimentary shutter speed of 1/2 sec We are at Don's handheld, Super SteadyShot limit (YMMV)... the noise is "acceptable", but this is hard work. I'm literally having to "bake the shot" ... and God forbid anything even thinks of moving ... or even breathing.

Now, taking the same Ev shot at f/1.8 ... that is 3 & 1/3rds f-stops wider than f/5.6.

In effect, I can use ISO-200 at 1/20 sec. (a solid steady shot) and effectively eliminate the dark noise. Almost taking images with impunity. Even an intro-DSLR with this lens could do a bang-up job, because ... you are out of the noise! (IMO: Best solution for images using an intro-camera -> better glass. You can always move to a better body, later. Glass always is what it is, not matter what the body. )

I figure if flash is verboten ... this is the next best thing.

Now, there are those who would argue to use 10mm @ f/4, which buys back an f-stop of light ... and then crop. Yeah ... there is that, but at 10mm, you can introduce some pretty nasty distortion, too. If you don't believe it, go take some 10mm & 20mm shots, alternating back and forth ... have fun. Then -> post process and see how much work there is straightening out 10mm-shots and make them look like 20mm-ones. It will be educational.

One thing to bear in mind ... advantage-wise with a 10-20mm zoom ... the Field of View is from 102.4° to 63.8° ... 102.4° covers a lot of ground.

Last edited by DonSchap; 05-30-2009 at 06:13 PM.

Don Schap - BFA, Digital Photography A Photographer Is ForeverLook, I did not create the optical laws of the Universe ... I simply learned to deal with them.
Remember: It is usually the GLASS, not the camera (except for moving to Full Frame), that gives you the most improvement in your photography.flickr® & Sdi

There are some striking differences in effect with the 20mm f/1.8 mounted on the A900 body. Basically, the DOF increases under the same situation. ...

As you can easily see ... not only do you get you get 30-degrees more Field of View (FoV) and nearly 2x the DOF at 10-feet away ... but, you also get a whole bunch more DOF at 20-feet ... almost 10 times more!

If you needed a reason to buy the A900 ... this is a decent one. Plus, if you put the α900 in "CROP" mode, you can whack that DOF right back down to the first diagram ... and get some bokeh in that "bright" shot. It's like having a 20mm and a 30mm lens on your camera.

Thanks Don for the great info. I have yet to use the APS-C function on my α900. I might just try it, if only to figure out the resulting MP resolution - the manual doesn't say what MP resolution you get when the APS-C function is on.